Boost Regulator Having Adaptive Dead Time

ABSTRACT

A boost regulator that selectively operates in an asynchronous mode, a synchronous mode, or an adaptive mode. In the adaptive mode, the boost mode regulator controls a high side switch according to an adaptive dead time. Adaptive mode allows the boost regulator to operate more efficiently than in asynchronous mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

BACKGROUND

The disclosure relates to boost regulators, and in particular, tooperating a boost regulator in various operational modes.

Unless otherwise indicated herein, the approaches described in thissection are not admitted to be prior art by inclusion in this section.

A boost regulator is a DC-to-DC (direct current) power converter with anoutput voltage greater than its input voltage. A boost regulator mayalso be called a boost converter or a (voltage) step-up converter. Aboost regulator is a class of switched-mode power supply (SMPS)containing at least two semiconductor elements (e.g., a diode and atransistor) and at least one energy storage element (e.g., a capacitor,inductor, or the two in combination). Filters made of capacitors(sometimes in combination with inductors) may be added to the output ofthe boost regulator to reduce output voltage ripple.

Power for the boost regulator can come from any suitable DC sources,such as batteries, solar panels, rectifiers and DC generators. A processthat changes one DC voltage to a different DC voltage is called DC to DCconversion. A boost regulator is sometimes called a step-up convertersince it “steps up” the source voltage. Since power (P=V*I) must beconserved, the output current is lower than the input current.

SUMMARY

The present disclosure is directed to improving the efficiency of theoperation of boost converters.

In one embodiment, a boost regulator includes a low side switch, a highside switch, and a boost mode regulator. The low side switch is coupledto a switching node, and the high side switch is coupled to theswitching node and to an output node. The boost mode regulator controlsthe low side switch and the high side switch to selectively operate inone of an asynchronous mode, a synchronous mode, and an adaptive mode.

According to a further embodiment, the boost mode regulator switches thelow side switch according to a duty cycle. The duty cycle is adjustable,and the boost mode regulator increases the duty cycle to increase anoutput voltage at the output node.

According to a further embodiment, in the synchronous mode, the boostmode regulator controls the low side switch and the high side switch tooperate such that the high side switch conducts when the low side switchdoes not conduct, and the high side switch does not conduct when the lowside switch conducts.

According to a further embodiment, in the asynchronous mode, the boostmode regulator controls the high side switch to not conduct, and theboost mode regulator switches the low side switch according to a dutycycle.

According to a further embodiment, the boost regulator has an inputvoltage and an output voltage. In the adaptive mode, the boost moderegulator controls the high side switch according to an adaptive deadtime. The adaptive dead time changes as a voltage difference between theinput voltage and the output voltage changes. In the adaptive mode, whenthe low side switch switches from conducting to not conducting, theboost mode regulator controls the high side switch to switch from notconducting to conducting after the adaptive dead time. In the adaptivemode, when the low side switch switches from not conducting toconducting, the boost mode regulator controls the high side switch toswitch from conducting to not conducting after the adaptive dead time.

According to a further embodiment, the boost regulator includes aninductor coupled to the switching node and to an input node. Accordingto a further embodiment, the boost regulator includes a battery coupledto the input node. According to a further embodiment, the output nodehas an output voltage, the high side switch has a diode drop voltagewhen the high side switch is not conducting, and the output voltagecorresponds to a switching voltage at the switching node less the diodedrop voltage when the high side switch is not conducting.

According to a further embodiment, the boost regulator is coupled to aninput node, and the boost regulator further comprises an analog timerand an adaptive dead time generator circuit. The analog timer generatesa comparison signal based on an input voltage at the input node and anoutput voltage at the output node. The adaptive dead time generatorcircuit receives the comparison signal and generates a control signal tocontrol the high side switch. The control signal includes an adaptivedead time according to the comparison signal.

According to a further embodiment, when a voltage difference between aninput voltage and an output voltage of the boost regulator is below athreshold, the boost regulator controls the low side switch and the highside switch to operate in the asynchronous mode.

According to a further embodiment, when a voltage difference between aninput voltage and an output voltage of the boost regulator is above athreshold, the boost regulator controls the low side switch and the highside switch to operate in the synchronous mode.

According to a further embodiment, when a voltage difference between aninput voltage and an output voltage of the boost regulator is between afirst threshold and a second threshold, the boost regulator controls thelow side switch and the high side switch to operate in the adaptivemode.

In another embodiment, a method of operating a boost regulator includesdetecting a voltage difference between an input voltage and an outputvoltage of the boost regulator. The method further includes when thevoltage difference is below a first threshold, operating the boostregulator in an asynchronous mode. The method further includes when thevoltage difference is above a second threshold, operating the boostregulator in a synchronous mode. The method further includes when thevoltage difference is between the first threshold and the secondthreshold, operating the boost regulator in an adaptive mode.

According to a further embodiment, the method includes controlling a lowside switch and a high side switch of the boost regulator to selectivelyoperate in the asynchronous mode, the synchronous mode, and the adaptivemode.

According to a further embodiment, the method includes switching a lowside switch of the boost regulator according to a duty cycle. The dutycycle is adjustable, and the boost regulator increases the duty cycle toincrease the output voltage.

According to a further embodiment, operating the boost regulator in thesynchronous mode comprises controlling a low side switch and a high sideswitch to operate such that the high side switch conducts when the lowside switch does not conduct, and the high side switch does not conductwhen the low side switch conducts.

According to a further embodiment, operating the boost regulator in theasynchronous mode comprises controlling a high side switch to notconduct, and switching a low side switch according to a duty cycle.

According to a further embodiment, operating the boost regulator in theadaptive mode comprises determining an adaptive dead time based on thevoltage difference. The adaptive dead time changes as the voltagedifference changes. When a low side switch switches from conducting tonot conducting, operating the boost regulator in the adaptive modefurther comprises controlling a high side switch to switch from notconducting to conducting after the adaptive dead time. When the low sideswitch switches from not conducting to conducting, operating the boostregulator in the adaptive mode further comprises controlling the highside switch to switch from conducting to not conducting after theadaptive dead time.

In another embodiment, a boost regulator includes means for detecting avoltage difference between an input voltage and an output voltage of theboost regulator, and means for selectively operating the boost regulatorin one of an asynchronous mode, a synchronous mode, and an adaptivemode, according to the voltage difference.

According to a further embodiment, in the synchronous mode, the meansfor selectively operating the boost regulator controls a low side switchand a high side switch to operate such that the high side switchconducts when the low side switch does not conduct, and the high sideswitch does not conduct when the low side switch conducts.

According to a further embodiment, in the asynchronous mode, the meansfor selectively operating the boost regulator controls a high sideswitch to not conduct, and the means for selectively operating the boostregulator switches a low side switch according to a duty cycle.

According to a further embodiment, in the adaptive mode, the means forselectively operating the boost regulator determines an adaptive deadtime based on the voltage difference. The adaptive dead time changes asthe voltage difference changes. When a low side switch switches fromconducting to not conducting, the means for selectively operating theboost regulator controls a high side switch to switch from notconducting to conducting after the adaptive dead time. When the low sideswitch switches from not conducting to conducting, the means forselectively operating the boost regulator controls the high side switchto switch from conducting to not conducting after the adaptive deadtime.

In another embodiment, an electronic device includes a battery, aninductor, a load and a boost regulator. The battery is coupled to aninput node, the inductor is coupled to the input node and to a switchingnode, and the load is coupled to an output node. The boost regulatorincludes a low side switch coupled to the switching node, a high sideswitch coupled to the switching node and to the output node, and a boostmode regulator that controls the low side switch and the high sideswitch to selectively operate in one of an asynchronous mode, asynchronous mode, and an adaptive mode.

According to a further embodiment, the boost regulator begins in theasynchronous mode, transitions to the adaptive mode when a voltage ofthe battery falls below a first threshold, and transitions to thesynchronous mode when the voltage of the battery falls below a secondthreshold.

According to a further embodiment, the boost regulator begins in thesynchronous mode, transitions to the adaptive mode when a voltage of thebattery rises above a first threshold, and transitions to theasynchronous mode when the voltage of the battery rises above a secondthreshold.

According to a further embodiment, the boost regulator begins in theasynchronous mode, transitions to the adaptive mode when a voltage ofthe load rises above a first threshold, and transitions to thesynchronous mode when the voltage of the load rises above a secondthreshold.

According to a further embodiment, the boost regulator begins in thesynchronous mode, transitions to the adaptive mode when a voltage of theload falls below a first threshold, and transitions to the asynchronousmode when the voltage of the load falls below a second threshold.

According to a further embodiment, in the adaptive mode, the boost moderegulator controls the high side switch according to an adaptive deadtime. The adaptive dead time decreases as a voltage of the batterydecreases. The adaptive dead time increases as a voltage of the batteryincreases.

According to a further embodiment, the battery has a battery voltage andthe load has a load voltage. In the adaptive mode, the boost moderegulator controls the high side switch according to an adaptive deadtime. The adaptive dead time changes as a voltage difference between thebattery voltage and the load voltage changes. In the adaptive mode, whenthe low side switch switches from conducting to not conducting, theboost mode regulator controls the high side switch to switch from notconducting to conducting after the adaptive dead time. In the adaptivemode, when the low side switch switches from not conducting toconducting, the boost mode regulator controls the high side switch toswitch from conducting to not conducting after the adaptive dead time.

The following detailed description and accompanying drawings provide abetter understanding of the nature and advantages of the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

With respect to the discussion to follow and in particular to thedrawings, it is stressed that the particulars shown represent examplesfor purposes of illustrative discussion, and are presented in the causeof providing a description of principles and conceptual aspects of thepresent disclosure. In this regard, no attempt is made to showimplementation details beyond what is needed for a fundamentalunderstanding of the present disclosure. The discussion to follow, inconjunction with the drawings, make apparent to those of skill in theart how embodiments in accordance with the present disclosure may bepracticed. In the accompanying drawings:

FIG. 1 is a diagram of a boost regulator 100.

FIG. 2 is a diagram showing the adaptive dead time, in the adaptivemode.

FIG. 3 is a graph showing an example of the adaptive dead time.

FIG. 4A and FIG. 4B are graphs that illustrate the different dead timesthat result from different input voltages Vin, within the adaptive mode.

FIG. 5 is a block diagram of a control signal generator 500 for the highside switch 110 (see FIG. 1).

FIG. 6 is a circuit diagram showing more details of the control signalgenerator 500 (see FIG. 5).

FIG. 7 is a block diagram of a boost regulator 700.

FIG. 8 is a graph showing the efficiency comparison between adaptivemode and asynchronous mode for a boost regulator.

FIG. 9 is a flowchart of a method 900 of operating a boost regulator.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerousexamples and specific details are set forth in order to provide athorough understanding of the present disclosure. It will be evident,however, to one skilled in the art that the present disclosure asexpressed in the claims may include some or all of the features in theseexamples, alone or in combination with other features described below,and may further include modifications and equivalents of the featuresand concepts described herein.

The present disclosure uses the terms “conducting” and “not conducting”,with reference to a switch (such as a transistor). A synonymous term forconducting is “on”, and a synonymous term for not conducting is “off”.An n-channel metal oxide semiconductor (NMOS) device is on when its gateis high, and is off when its gate is low. A p-channel MOS (PMOS) deviceis on when its gate is low, and is off when its gate is high. An exampleof an NMOS device is an n-channel field effect transistor (NFET), and anexample of a PMOS device is a p-channel field effect transistor (PFET).

The present disclosure uses the terms “synchronous mode”, “asynchronousmode” and “adaptive mode”. In brief, these terms relate to therelationships between the low side switch and the high side switch inthe boost regulator. These terms are defined and described in moredetail in subsequent sections. However, these terms differ from, and arenot to be considered the same as, the term “continuous mode” and theterm “discontinuous mode”. In continuous mode, the current through theinductor in the boost regulator never falls to zero. In discontinuousmode, the inductor may be completely discharged before the end of awhole commutation cycle, and the current through the inductor falls tozero during part of the period. Thus, continuous mode and discontinuousmode relate to the relationship between the current and the inductor,not to the relationships between the low side switch and the high sideswitch.

FIG. 1 is a diagram of a boost regulator 100. The boost regulator 100includes an input capacitor 102, an output capacitor 104, an inductor106, a low side switch 108, a high side switch 110, and a boost moderegulator 112. An input node 120, a switching node 122, and an outputnode 124 are also shown. The input node 120 connects to a source (e.g.,a battery) having an input voltage Vin, and the output node 124 connectsto a load having an output voltage Vout.

The input capacitor 102 reduces ripple of the input voltage Vin at theinput node 120, and the output capacitor 104 reduces ripple of theoutput voltage Vout at the output node 124.

The low side switch 108 may be an NMOS transistor, and the high sideswitch 110 may be a PMOS transistor. As an alternative, the low sideswitch 108 may be a PMOS transistor. As another alternative, the highside switch 110 may be an NMOS transistor. The low side switch 108 andthe high side switch 110 may also be made using other types oftransistors or circuit structures.

The high side switch 110 includes a diode structure 130. The diodestructure 130 may be a body diode of the high side switch 110, or may bea diode in parallel with the high side switch 110. The diode structure130 allows current to flow from the switching node 122 to the outputnode 124 when the high side switch 110 is off. The diode structure 130has a diode drop voltage (e.g., 0.6 V), so the output voltage Vout atthe output node 124 will be slightly less than the voltage at theswitching node 122. Thus, the diode drop voltage allows the inputvoltage Vin (e.g., the battery voltage) at the input node 120 to behigher than the output voltage Vout at the output node 124 (e.g., theload voltage).

The inductor 106, the low side switch 108, and the high side switch 110operate together to perform the boost. The inductor 106 resists changesin current by creating and destroying a magnetic field. When the lowside switch 108 is closed, current flows through the inductor 106 fromthe input node 120 to the switching node 122, and the inductor 106stores some energy by generating a magnetic field. The polarity of theleft side of the inductor 106 is positive. When the low side switch 108is opened, current will be reduced as the impedance is higher. Themagnetic field previously created will be destroyed to maintain thecurrent flow from the switching node 122 to the output node 124. Thusthe polarity will be reversed (e.g., the left side of the inductor 106will be negative now). As a result, two sources will be in series (e.g.,the battery and the inductor 106), causing a higher voltage to chargethe output capacitor 104 through the high side switch 110.

In general, the boost regulator 100 boosts the voltage of the source toa desired level for the operation of the load. Note that the boostregulator 100 operates dynamically (adaptively, responsively, etc.). Forexample, the source voltage (input voltage Vin) may decrease over timedue to the battery becoming discharged. The source voltage may increaseover time due to the battery being recharged. The load (output voltageVout) may increase, or decrease, as various components of the load areswitched on or off. For example, the load of a mobile telephone may varyaccording to whether the screen is on or off, the cellular radio is onor off, the wireless radio is on or off, etc. The boost regulator 100operates to boost the voltage as appropriate for all these conditions asthey occur over time. The boost mode regulator 112 generally controlsthe operation of the boost regulator 100, by controlling the low sideswitch 108 and the high side switch 110.

The boost regulator 100 operates in one of three modes, depending on howmuch boost is needed (e.g., the difference between the output voltageVout and the input voltage Vin). The three modes are the synchronousmode, the asynchronous mode, and the adaptive mode.

Synchronous Mode

Synchronous mode is used when more boost is needed (e.g., when thebattery is not fully charged). In synchronous mode, the low side switch108 and the high side switch 110 operate in synchrony, such that thehigh side switch 110 conducts when the low side switch 108 does notconduct, and the high side switch 110 does not conduct when the low sideswitch 108 conducts.

The amount of boost provided is determined by the duty cycle of the lowside switch 108. The duty cycle represents the fraction of thecommutation period during which the low side switch 108 is on. ThereforeD ranges between 0 (the low side switch 108 is never on) and 1 (the lowside switch 108 is always on). During the off-state, the low side switch108 is open, so the current from the inductor 106 flows from theswitching node 122 to the output node 124 (to the load). The equationfor the duty cycle is as follows:

$D = {1 - \frac{Vin}{Vout}}$

The above equation shows that the output voltage Vout is always higherthan the input voltage Vin (as the duty cycle goes from 0 to 1), andthat it increases with D, theoretically to infinity as D approaches 1.(Note that this analysis does not account for the diode drop of the highside switch 110, and does not account for the physical constraints ofactual circuits.) This is why the boost regulator 100 is sometimesreferred to as a step-up converter.

In general, the boost mode regulator 112 switches the low side switch108 and the high side switch 110 according to the duty cycle. The dutycycle is adjustable, and the boost mode regulator 112 increases the dutycycle to increase the output voltage Vout at the output node 124. Theboost regulator 100 may be used in devices where a battery provides theinput voltage Vin. As the battery loses charge and the input voltage Vindrops, more boost is needed, so the boost mode regulator 112 increasesthe duty cycle.

Asynchronous Mode

Asynchronous mode is used when less boost (or no boost) is needed (e.g.,when the battery is fully charged). In the asynchronous mode, the boostmode regulator 112 controls the high side switch 110 to not conduct(e.g., fixed off), and the boost mode regulator 112 switches the lowside switch 108 according to the duty cycle. As discussed above, theduty cycle is adjustable according to the amount of boost desired. Ingeneral, in asynchronous mode, the duty cycle will be low, since lessboost (or no boost) is needed. The duty cycle being low means the lowside switch 108 is conducting only a small minority of the time, sinceless boost is needed.

In asynchronous mode (e.g., at higher battery input voltage levels), thelow side switch 108 is initially turned on, and current through theinductor 106 increases (ramps up). When the low side switch 108 isturned off, it is desirable to have the current ramp back down to somenominal value. In many applications, when the battery is fully chargedand at a peak input voltage Vin, there will be very little voltage dropbetween Vin and the output voltage Vout (i.e., voltage boosting ismostly required as the battery voltage drops). Thus, the forward voltagedrop on the diode structure 130 may be used to increase the voltage onthe switching node 122 so that the current can ramp back down when thelow side switch 108 is turned off. However, the forward voltage drop onthe diode structure 130 decreases the efficiency by up to approximately10-15%. The adaptive mode, discussed below, is directed to improvingthis efficiency.

Adaptive Mode

Adaptive mode is used when less boost is needed than in synchronousmode, but more boost is needed than in asynchronous mode. That is,adaptive mode is between synchronous mode and asynchronous mode. In theadaptive mode, the boost mode regulator 112 controls the high sideswitch 110 according to an adaptive dead time. The adaptive dead timechanges (adapts, adjusts, responds, is dynamic, etc.) as the voltagedifference between the input voltage and the output voltage changes.When the low side switch 108 switches from conducting to not conducting,the boost mode regulator 112 controls the high side switch 110 to switchfrom not conducting to conducting after the adaptive dead time. When thelow side switch 108 switches from not conducting to conducting, theboost mode regulator 112 controls the high side switch 110 to switchfrom conducting to not conducting after the adaptive dead time.

As discussed above, the boost mode regulator 112 controls the low sideswitch 108 to switch according to the duty cycle. As discussed above,the duty cycle is adjustable (responsive, adaptive, dynamic, changeable,etc.) according to the amount of boost desired. In general, in adaptivemode, the duty cycle will be low, similar to asynchronous mode.

FIG. 2 is a diagram showing the adaptive dead time, in the adaptivemode. The signal 202 is the gate control signal for the low side switch108 (see FIG. 1), and the signal 204 is the gate control signal for thehigh side switch 110. The signal 202 corresponds to the gate controlsignal for an NMOS device, so the high state corresponds to on(conducting) and the low state corresponds to off (not conducting). Thesignal 204 corresponds to the gate control signal for a PMOS device, sothe high state corresponds to off (not conducting) and the low statecorresponds to on (conducting).

The period Ts is the commutation period, the period Ton is the time thelow side switch 108 (see FIG. 1) is on, and the period Tdead is the deadtime. Thus, the high side switch 110 is off for the period Ton plus thedead time Tdead. The duty cycle is then the ratio of Ton to Ts. The deadtime Tdead is referred to as an adaptive dead time because the boostmode regulator 112 adjusts it according to changes in Vin (or moreprecisely, according to changes in the difference between Vout and Vin).For example, the dotted line for the signal 204 shows that the dead timeis increased, in response to Vin being increased.

As mentioned above, the boost regulator 100 (see FIG. 1) uses theadaptive dead time Tdead to control the high side switch 110. As can beseen in FIG. 2, the dead time Tdead is the time the high side switch 110remains non-conducting (signal 204) after the low-side switch 108switches to non-conducting (signal 202), to provide a diode voltageabove Vout so the current through the inductor 106 ramps down. As thebattery loses charge, Vin decreases, and the boost regulator 100operates in adaptive mode, where the high side switch 110 remains offfor a minimum time to allow the current through the inductor 106 to rampdown. As Vin continues to decrease, the time that the diode voltage isneeded also decreases. Thus, as Vin decreases, the dead time Tdead alsodecreases. (Or more generally, as the difference between Vout and Vinincreases, the dead time Tdead decreases.)

Consider the following example of the modes of operation of the boostregulator 100 (see FIG. 1). Initially there is little (or no) differencebetween Vout and Vin, so no boost is required, and the boost regulator100 operates in asynchronous mode. (In fact, the boost regulator 100 maymake use of the diode drop of the diode structure 130 when operating inasynchronous mode, due to the battery having a higher voltage (Vin) thanthe load (Vout).) For example, when the battery is fully charged, theboost regulator 100 operates in asynchronous mode (e.g., the high-sideswitch 110 is fixed as non-conducting), where the diode structure 130 iskept in the circuit during an entire cycle (because the diode voltage isneeded for the full cycle to reduce the current through the inductor106). As the battery voltage Vin decreases, the voltage differencebetween Vin and Vout increases. When the voltage difference increasesabove a first threshold, the boost regulator 100 transitions from theasynchronous mode to the adaptive mode. When first entering the adaptivemode from the asynchronous mode, the dead time Tdead starts at itsmaximum, then adaptively decreases as the voltage difference continuesto increase. In the adaptive mode, the diode voltage is only in thecircuit for the time necessary to cause the current through the inductor106 to ramp down, but is out of the circuit as soon as possible toimprove efficiency. When the voltage difference increases above a secondthreshold, the dead time Tdead on each switching cycle reaches zero, andthe boost regulator 100 transitions to synchronous mode.

As a variation on the above example, consider that the boost regulator100 (see FIG. 1) may start in synchronous mode (according to the voltagedifference between Vin and Vout), for example due to the battery notbeing fully charged. Next, the battery is connected to a chargingdevice, so the charge in the battery begins to increase, and the voltagedifference between Vin and Vout begins to decrease. After the voltagedifference decreases below a first threshold, the boost regulator 100transitions from synchronous mode to adaptive mode. Initially the deadtime Tdead is at its minimum, but as the charge in the battery continuesto increase (and the voltage difference continues to decrease), the deadtime Tdead adaptively increases. After the voltage difference decreasesbelow a second threshold, the boost regulator 100 transitions fromadaptive mode to asynchronous mode.

FIG. 3 is a graph showing an example of the adaptive dead time. In thisexample, the output voltage Vout is fixed at 4.6 V, the diode voltage is0.6 V, and the switching frequency is 1.6 MHz. The x-axis is the inputvoltage Vin, and the y-axis is the duration of the dead time in ns. Theline 302 shows the dead time as it changes with (adapts to) the changinginput voltage Vin. As discussed above regarding FIG. 1, the dead time isused to control the high side switch 110. Note the two thresholds V1 andV2. When the input voltage Vin is above V2 (about 4.79 V), the boostregulator 100 operates in asynchronous mode, and the high side switch110 is not conducting. When the input voltage Vin is below V1 (about4.22 V), the boost regulator 100 operates in synchronous mode; the highside switch 110 is conducting when the low side switch 108 is notconducting, and the high side switch 110 is not conducting when the lowside switch 108 is conducting. When the input voltage Vin is between V1and V2, the boost regulator 100 operates in adaptive mode. Nearer to V2,the dead time is higher (e.g., 600 ns); as the input voltage Vindecreases toward V1, the dead time decreases. Similarly, as the inputvoltage Vin increases from V1 toward V2, the dead time increases.

The line 304 shows how the control signal for the high side switch 110(see FIG. 1) would be modified in the absence of the adaptive dead time(e.g., in the absence of adaptive mode, with only synchronous andasynchronous modes available). When the input voltage Vin is above V2,the boost regulator operates in asynchronous mode, and the high sideswitch 110 is not conducting. As the input voltage Vin decreases from V2to V1, the high side switch 110 is still fixed as not conducting. Thatis, in the absence of adaptive mode, the boost regulator would useasynchronous mode between V1 and V2. Then as the input voltage Vindecreases below V1, the boost regulator operates in synchronous mode. Asdescribed above, the diode structure 130 (see FIG. 1) is in the circuitwhen the high side switch 110 is not conducting, so between V1 and V2,the line 304 puts the diode structure 130 into the circuit more oftenthan the line 302, so a boost regulator lacking the adaptive mode isless efficient.

The example of FIG. 3 can be generalized to describe a voltagedifference between the output voltage Vout and the input voltage Vin (asopposed to the fixed output voltage Vout described above). The outputvoltage Vout may change as the load changes, for example, as variouscomponents of the load are turned on or off (e.g., screen, cellularradio, wireless radio, etc.). When the voltage difference is below afirst threshold, the boost regulator controls the low side switch 108and the high side switch 110 to operate in the asynchronous mode. (Ascompared to FIG. 3, the voltage difference is small when the inputvoltage Vin is large, e.g., when Vin is above V2.) When the voltagedifference is above a second threshold, the boost regulator controls thelow side switch 108 and the high side switch 110 to operate in thesynchronous mode. (As compared to FIG. 3, the voltage difference islarge when the input voltage Vin is small, e.g., when Vin is below V1.)When the voltage difference is between the first threshold and thesecond threshold, the boost regulator controls the low side switch 108and the high side switch 110 to operate in the adaptive mode. (Ascompared to FIG. 3, the voltage difference is between the thresholdswhen the input voltage Vin is between V1 and V2.)

FIG. 4A and FIG. 4B are graphs that illustrate the different dead timesthat result from different input voltages Vin, within the adaptive mode.In FIG. 4B the input voltage Vin2 (462) is a bit higher than the inputvoltage Vin1 (412) of FIG. 4A, and correspondingly the dead time Tdead2of FIG. 4B is longer than the dead time Tdead1 of FIG. 4A.

FIG. 4A shows four waveforms: the low side switch (NFET) control signal402, the high side (PFET) switch control signal 404, the switching nodeand input waveforms 406, and the inductor current waveform 408. Thedotted lines show times t1, t2, t3 and t4 on the x-axes.

The low side switch control signal 402 controls the low side switch(e.g., 108 in FIG. 1). The low side switch control signal 402 has acommutation period Ts (0 to t4). The low side switch control signal 402is high for the time period Ton (0 to t2), which corresponds to the lowside switch being on (conducting). The low side switch is off (notconducting) the remainder of the commutation period Ts (t2 to t4).

The high side switch control signal 404 controls the high side switch(e.g., 110 in FIG. 1). The high side switch control signal 404 is highfor the time period Ton plus the dead time Tdead1 (t1 to t3), whichcorresponds to the high side switch being off (not conducting). The highside switch is on (conducting) for the remainder of the commutationperiod Ts (t3 to t4).

The switching node and input waveforms 406 include the switching nodewaveform 410 and the input voltage Vin waveform 412. The switching nodewaveform 410 corresponds to the voltage at the switching node 122 (seeFIG. 1), and the input voltage Vin waveform 412 corresponds to thevoltage at the input node 120 (see FIG. 1). The input voltage Vinwaveform 412 is shown staying at a constant level (and the outputvoltage Vout is also assumed to be unchanging), resulting in theselected dead time Tdead1 as shown. Prior to t1, the switching nodewaveform 410 is at the output voltage Vout due to the high side switchcontrol signal 404 being low (e.g., the high side switch 110 in FIG. 1is conducting). At t1, the switching node waveform 410 goes to zero dueto the low side switch control signal 402 being high (e.g., the low sideswitch 108 in FIG. 1 is conducting). At t2, the switching node waveform410 goes to the output voltage Vout plus the diode drop voltage Vdiode,due to the low side switch control signal 402 being low and the highside switch control signal 404 being high. At t3, the switching nodewaveform 410 goes to the output voltage Vout due to the low side switchcontrol signal 402 being low and the high side switch control signal 404being low. At t4, the switching node waveform 410 goes to zero, asdiscussed above for t1.

The inductor current waveform 408 shows the current through the inductor(e.g., 106 in FIG. 1). At t1, the inductor current waveform 408 startsat its minimum due to the low side switch control signal 402 being lowprior to t1. From t1 to t2, the inductor current waveform 408 increasesdue to the low side switch control signal 402 being high. From t2 to t3,the inductor current waveform 408 decreases at a first rate, due to thelow side switch control signal 402 being low and the high side switchcontrol signal 404 being high (due to the dead time Tdead1). From t3 tot4, the inductor current waveform 408 decreases at a second rate, due tothe low side switch control signal 402 being low and the high sideswitch control signal 404 being low. Note that the first rate is greaterthan the second rate due to the diode structure 130 (see FIG. 1) beingin the circuit during the dead time Tdead1. At t4, the inductor currentwaveform 408 is again at its minimum, as discussed above for t1.

FIG. 4B shows four waveforms: the low side switch control signal 452,the high side switch control signal 454, the switching node and inputwaveforms 456, and the inductor current waveform 458. These waveformsare similar to those in FIG. 4A, as are the times t1, t2, t3 and t4 onthe x-axes. The main difference is that in FIG. 4B the input voltageVin2 (the waveform 462) is a bit higher than the input voltage Vin1 ofFIG. 4A (the waveform 412), and correspondingly the dead time Tdead2 (t2to t3) of FIG. 4B is longer than the dead time Tdead1 (t2 to t3) of FIG.4A.

An additional difference concerns the high side switch control signal454. Since the dead time Tdead2 of FIG. 4B is longer than the dead timeTdead1 of FIG. 4A, the high side switch control signal 454 is high forlonger in FIG. 4B as compared to FIG. 4A. This increases the distancebetween t2 and t3 in FIG. 4B as compared to FIG. 4A.

Another difference concerns the switching node and input waveforms 456.The switching node waveform 450 stays at the output voltage Vout plusthe diode drop voltage Vdiode for longer as compared to FIG. 4A. Thiscauses the inductor current waveform 458 to decrease at the first rate(t2 to t3) for longer as compared to FIG. 4A, and to decrease at thesecond rate (t3 to t4) for shorter as compared to FIG. 4A.

FIG. 5 is a block diagram of a control signal generator 500 for the highside switch 110 (see FIG. 1). The control signal generator 500 may be acomponent of, or otherwise connect with, the boost mode regulator 112(see FIG. 1). The control signal generator 500 receives the outputvoltage signal Vout from the output node 124 (see FIG. 1), the inputvoltage signal Vin from the input node 120, and an input control signal502 (Pgate_origin). The control signal generator 500 generates an outputcontrol signal 504 (Pgate_prolong) that controls the high side switch110 (see FIG. 1). In general, the output control signal 504 correspondsto the input control signal 502 plus the dead time Tdead.

The control signal generator 500 includes an analog timer 510 and anadaptive dead time generator 512. The analog timer 510 generates acomparison signal 514 based on the input voltage Vin and the outputvoltage Vout. The adaptive dead time generator 512 receives thecomparison signal 514 and generates the output control signal 504.

FIG. 6 is a circuit diagram showing more details of the control signalgenerator 500 (see FIG. 5). The adaptive dead time generator 512 may beimplemented with an OR gate 602. The analog timer 510 may be implementedwith two switches SW1 and SW2, a current source I0, a capacitor Ct,resistors R3 and R4, and a comparator 604. The resistor R3 may be avariable resistor. The input control signal 502′ (Pgate_origin_b) is theinverting signal of the input control signal 502 (Pgate_origin). Thesignals 502 and 502′ control the switches SW1 and SW2.

In general, the difference between Vout and Vin determines the deadtime. The dead time is inversely proportional to the difference: Whenthe difference is relatively small, the dead time is relatively large,and when the difference is relatively large, the dead time is relativelysmall. More specifically, the adaptive dead time achieved by the controlsignal generator 500 is according to the following equation:

$T_{{dead}\_ {real}} = {\frac{C_{t}}{I_{0}} \cdot \left( {V_{i\; n} - {V_{out} \cdot \frac{R_{4}}{R_{4} + R_{3}}}} \right)}$

In this equation, the voltage difference refers not only to thedifference between the input voltage Vin and the output voltage Vout,but also to the difference as modified according to the variousparameters. The parameters for Ct, I0, R3 and R4 may be selected inorder for the circuit 500 to implement the curve of the line 302 (seeFIG. 3). Alternatively, the parameters may be adjusted as desired toimplement other ways of calculating the dead time.

FIG. 7 is a block diagram of a boost regulator 700. The boost regulator700 is similar to the boost regulator 100 (see FIG. 1), with similarcomponents having similar reference numbers (e.g., the low side switch108, the high side switch 110, etc.). The diode structure 130 (seeFIG. 1) is a component of the high side switch 110 and is not shown. Ingeneral, FIG. 7 shows more details of the components that make up theboost mode regulator 112 (see FIG. 1).

The input node 120 connects to a battery 702 as the source, and theoutput node 124 connects to a load 704, represented as a current sink.The boost regulator 700 may be a component of, or connected to, anelectronic device such as a mobile telephone, a portable computer, atablet computer, etc. The boost regulator 700 includes the controlsignal generator 500 (see FIG. 5) and related components, resistors R1and R2, a clock signal generator 710, a boost controller 712, a low sideswitch control logic and driver circuit 714, a high side switch controllogic circuit 716, and a high side switch driver circuit 718.

The clock signal generator 710 generates a clock signal for the boostcontroller 712, for example to generate the clock signals for timing thecommutation period, the duty cycle, the dead time, or the timing forturning the switches on and off, etc. The boost controller 712 receivesa feedback voltage Vfb that is based on the output voltage Vout (notethe connections to the resistors R1 and R2). The boost controller 712uses the feedback voltage Vfb to generate control signals for the lowside switch control logic and driver circuit 714 and the high sideswitch control logic circuit 716, for example to control the duty cyclesfor switching the switches 108 and 110. The low side switch controllogic and driver circuit 714 controls the switching of the low sideswitch 108.

The high side switch control logic circuit 716 generates thePgate_origin signal 502 for the control signal generator 500 (see FIG.5). The analog timer 510 receives the input voltage Vin from the inputnode 120. The adaptive dead time generator 512 receives the Pgate_originsignal 502 and generates the Pgate_prolong signal 504 for the high sideswitch driver circuit 718. The high side switch driver circuit 718controls the switching of the high side switch 110.

FIG. 8 is a graph showing the efficiency comparison between adaptivemode and asynchronous mode for a boost regulator. For example, a boostregulator lacking adaptive mode would instead use asynchronous mode,resulting in the inefficiency discussed above (e.g., regarding FIG. 3).In FIG. 8, the x-axis is the input voltage Vin in volts, the outputvoltage Vout is fixed at 4.6 V, and the y-axis is the efficiency as apercentage. The line 802 shows the efficiency of asynchronous mode, andthe line 804 shows the efficiency of adaptive mode. When the inputvoltage Vin is below about 4.2 V, the efficiencies are the same (around94.5%). When the input voltage Vin is around 4.25 V, the efficiencydifference is the largest, with adaptive mode (line 804) being around94% efficient and asynchronous mode (line 802) being around 82%efficient. As the input voltage Vin increases, the efficiency of theadaptive mode (line 804) decreases, with the efficiencies becoming equalwhen the input voltage Vin is above about 4.7 V (off the right edge ofthe graph).

FIG. 9 is a flowchart of a method 900 of operating a boost regulator(e.g., the boost regulator 100 of FIG. 1). The boost regulator includesa low side switch and a high side switch (e.g., 108 and 110 in FIG. 1).

At 902, a voltage difference is detected between an input voltage and anoutput voltage of the boost regulator. For example, the boost regulatormay detect the voltage difference using an analog timer (e.g., theanalog timer 510 of FIG. 6). The voltage difference need not be astraight subtraction, but may also be an equation as discussed above.Depending upon the detected voltage difference, the method 900 proceedsto one of 904, 906 and 908. For example, the boost mode regulator 112(see FIG. 1) may control the boost regulator to selectively operateaccording to 904, 906 or 908, for example by controlling the low sideswitch and the high side switch (e.g., 108 and 110 in FIG. 1).

At 904, when the voltage difference is below a first threshold, theboost regulator is operated in an asynchronous mode. For example, inFIG. 3, when the input voltage Vin is above V2, the voltage differenceis below a first threshold. The voltage difference need not be astraight subtraction, but may also be an equation as discussed above. Inasynchronous mode, the high side switch is controlled to not conduct,and the low side switch is switched according to a duty cycle.

At 906, when the voltage difference is above a second threshold, theboost regulator is operated in a synchronous mode. For example, in FIG.3, when the input voltage Vin is below V1, the voltage difference isabove a second threshold. The voltage difference need not be a straightsubtraction, but may also be an equation as discussed above. Insynchronous mode, the low side switch and the high side switch arecontrolled to operate such that the high side switch conducts when thelow side switch does not conduct, and the high side switch does notconduct when the low side switch conducts.

At 908, when the voltage difference is between the first threshold andthe second threshold, the boost regulator is operated in an adaptivemode. For example, in FIG. 3, when the input voltage Vin is between V1and V2, the voltage difference is between the first threshold and thesecond threshold. In adaptive mode, an adaptive dead time is determinedbased on the voltage difference. The voltage difference need not be astraight subtraction, but may also be an equation as discussed above.The adaptive dead time changes as the voltage difference changes. Whenthe low side switch switches from conducting to not conducting, the highside switch is controlled to switch from not conducting to conductingafter the adaptive dead time. When the low side switch switches from notconducting to conducting, the high side switch is controlled to switchfrom conducting to not conducting after the adaptive dead time.

After 904, 906 or 908, the method 900 returns to 902 in order tocontinuously detect the voltage difference and to switch modesaccordingly. Within the adaptive mode, as the method 900 is cyclingbetween 902 and 908, the dead time is adaptively adjusted according tothe voltage difference.

The method may further include switching the low side switch of theboost regulator according to a duty cycle. The duty cycle is adjustable,and the boost mode regulator increases the duty cycle to increase theoutput voltage. For example, the boost controller 712 (see FIG. 7)senses the output voltage Vout, and adjusts the duty cycle accordingly.

In summary, as discussed above, the adaptive mode improves theefficiency of the boost regulator, as compared to a boost regulatorlacking the adaptive mode (see also FIG. 8). The adaptive mode allowsthe boost regulator to operate more selectively regarding the forwardvoltage drop on the diode structure 130 (see FIG. 1) in the high sideswitch 110. In addition, the adaptive mode smooths out the transitionbetween synchronous mode and asynchronous mode, as otherwise the modetransition may create undesired overshoots or undershoots due to thesudden voltage change between the switching node 122 (see FIG. 1) andthe output node 124. Finally, when the high side switch 110 isimplemented with a PMOS transistor, and its body diode is used as thediode structure 130, a parasitic PNP bipolar junction transistor isturned on, injecting additional currents into the substrate, which hurtsthe efficiency and reliability; using the adaptive mode improves this.

The above description illustrates various embodiments of the presentdisclosure along with examples of how aspects of the particularembodiments may be implemented. The above examples should not be deemedto be the only embodiments, and are presented to illustrate theflexibility and advantages of the particular embodiments as defined bythe following claims. Based on the above disclosure and the followingclaims, other arrangements, embodiments, implementations and equivalentsmay be employed without departing from the scope of the presentdisclosure as defined by the claims.

What is claimed is:
 1. A boost regulator, comprising: a low side switchcoupled to a switching node; a high side switch coupled to the switchingnode and to an output node; and a boost mode regulator that controls thelow side switch and the high side switch to selectively operate in oneof an asynchronous mode, a synchronous mode, and an adaptive mode. 2.The boost regulator of claim 1, wherein the boost mode regulatorswitches the low side switch according to a duty cycle, wherein the dutycycle is adjustable, and wherein the boost mode regulator increases theduty cycle to increase an output voltage at the output node.
 3. Theboost regulator of claim 1, wherein in the synchronous mode, the boostmode regulator controls the low side switch and the high side switch tooperate such that the high side switch conducts when the low side switchdoes not conduct, and the high side switch does not conduct when the lowside switch conducts.
 4. The boost regulator of claim 1, wherein in theasynchronous mode, the boost mode regulator controls the high sideswitch to not conduct, and the boost mode regulator switches the lowside switch according to a duty cycle.
 5. The boost regulator of claim1, wherein the boost regulator has an input voltage and an outputvoltage, wherein in the adaptive mode, the boost mode regulator controlsthe high side switch according to an adaptive dead time, wherein theadaptive dead time changes as a voltage difference between the inputvoltage and the output voltage changes, wherein in the adaptive mode,when the low side switch switches from conducting to not conducting, theboost mode regulator controls the high side switch to switch from notconducting to conducting after the adaptive dead time, and wherein inthe adaptive mode, when the low side switch switches from not conductingto conducting, the boost mode regulator controls the high side switch toswitch from conducting to not conducting after the adaptive dead time.6. The boost regulator of claim 1, further comprising: an inductorcoupled to the switching node and to an input node.
 7. The boostregulator of claim 1, further comprising: an inductor coupled to theswitching node and to an input node; and a battery coupled to the inputnode.
 8. The boost regulator of claim 1, further comprising: an inductorcoupled to the switching node and to an input node; and a batterycoupled to the input node, wherein the output node has an outputvoltage, wherein the high side switch has a diode drop voltage when thehigh side switch is not conducting, and wherein the output voltagecorresponds to a switching voltage at the switching node less the diodedrop voltage when the high side switch is not conducting.
 9. The boostregulator of claim 1, wherein the boost regulator is coupled to an inputnode, the boost regulator further comprising: an analog timer thatgenerates a comparison signal based on an input voltage at the inputnode and an output voltage at the output node; and an adaptive dead timegenerator circuit that receives the comparison signal, and thatgenerates a control signal to control the high side switch, wherein thecontrol signal includes an adaptive dead time according to thecomparison signal.
 10. The boost regulator of claim 1, wherein when avoltage difference between an input voltage and an output voltage of theboost regulator is below a threshold, the boost regulator controls thelow side switch and the high side switch to operate in the asynchronousmode.
 11. The boost regulator of claim 1, wherein when a voltagedifference between an input voltage and an output voltage of the boostregulator is above a threshold, the boost regulator controls the lowside switch and the high side switch to operate in the synchronous mode.12. The boost regulator of claim 1, wherein when a voltage differencebetween an input voltage and an output voltage of the boost regulator isbetween a first threshold and a second threshold, the boost regulatorcontrols the low side switch and the high side switch to operate in theadaptive mode.
 13. A method of operating a boost regulator, the methodcomprising: detecting a voltage difference between an input voltage andan output voltage of the boost regulator; when the voltage difference isbelow a first threshold, operating the boost regulator in anasynchronous mode; when the voltage difference is above a secondthreshold, operating the boost regulator in a synchronous mode; and whenthe voltage difference is between the first threshold and the secondthreshold, operating the boost regulator in an adaptive mode.
 14. Themethod of claim 13, further comprising: controlling a low side switchand a high side switch of the boost regulator to selectively operate inthe asynchronous mode, the synchronous mode, and the adaptive mode. 15.The method of claim 13, further comprising: switching a low side switchof the boost regulator according to a duty cycle, wherein the duty cycleis adjustable, and wherein the boost regulator increases the duty cycleto increase the output voltage.
 16. The method of claim 13, whereinoperating the boost regulator in the synchronous mode comprises:controlling a low side switch and a high side switch to operate suchthat the high side switch conducts when the low side switch does notconduct, and the high side switch does not conduct when the low sideswitch conducts.
 17. The method of claim 13, wherein operating the boostregulator in the asynchronous mode comprises: controlling a high sideswitch to not conduct; and switching a low side switch according to aduty cycle.
 18. The method of claim 13, wherein operating the boostregulator in the adaptive mode comprises: determining an adaptive deadtime based on the voltage difference, wherein the adaptive dead timechanges as the voltage difference changes; when a low side switchswitches from conducting to not conducting, controlling a high sideswitch to switch from not conducting to conducting after the adaptivedead time; and when the low side switch switches from not conducting toconducting, controlling the high side switch to switch from conductingto not conducting after the adaptive dead time.
 19. A boost regulator,comprising: means for detecting a voltage difference between an inputvoltage and an output voltage of the boost regulator; and means forselectively operating the boost regulator in one of an asynchronousmode, a synchronous mode, and an adaptive mode, according to the voltagedifference.
 20. The boost regulator of claim 19, wherein in thesynchronous mode, the means for selectively operating the boostregulator controls a low side switch and a high side switch to operatesuch that the high side switch conducts when the low side switch doesnot conduct, and the high side switch does not conduct when the low sideswitch conducts.
 21. The boost regulator of claim 19, wherein in theasynchronous mode, the means for selectively operating the boostregulator controls a high side switch to not conduct, and the means forselectively operating the boost regulator switches a low side switchaccording to a duty cycle.
 22. The boost regulator of claim 19, whereinin the adaptive mode, the means for selectively operating the boostregulator determines an adaptive dead time based on the voltagedifference, wherein the adaptive dead time changes as the voltagedifference changes, and when a low side switch switches from conductingto not conducting, the means for selectively operating the boostregulator controls a high side switch to switch from not conducting toconducting after the adaptive dead time, and when the low side switchswitches from not conducting to conducting, the means for selectivelyoperating the boost regulator controls the high side switch to switchfrom conducting to not conducting after the adaptive dead time.
 23. Anelectronic device, comprising: a battery coupled to an input node; aninductor coupled to the input node and to a switching node; a loadcoupled to an output node; and a boost regulator, including: a low sideswitch coupled to the switching node, a high side switch coupled to theswitching node and to the output node, and a boost mode regulator thatcontrols the low side switch and the high side switch to selectivelyoperate in one of an asynchronous mode, a synchronous mode, and anadaptive mode.
 24. The electronic device of claim 23, wherein the boostregulator begins in the asynchronous mode, transitions to the adaptivemode when a voltage of the battery falls below a first threshold, andtransitions to the synchronous mode when the voltage of the batteryfalls below a second threshold.
 25. The electronic device of claim 23,wherein the boost regulator begins in the synchronous mode, transitionsto the adaptive mode when a voltage of the battery rises above a firstthreshold, and transitions to the asynchronous mode when the voltage ofthe battery rises above a second threshold.
 26. The electronic device ofclaim 23, wherein the boost regulator begins in the asynchronous mode,transitions to the adaptive mode when a voltage of the load rises abovea first threshold, and transitions to the synchronous mode when thevoltage of the load rises above a second threshold.
 27. The electronicdevice of claim 23, wherein the boost regulator begins in thesynchronous mode, transitions to the adaptive mode when a voltage of theload falls below a first threshold, and transitions to the asynchronousmode when the voltage of the load falls below a second threshold. 28.The electronic device of claim 23, wherein in the adaptive mode, theboost mode regulator controls the high side switch according to anadaptive dead time, wherein the adaptive dead time decreases as avoltage of the battery decreases.
 29. The electronic device of claim 23,wherein in the adaptive mode, the boost mode regulator controls the highside switch according to an adaptive dead time, wherein the adaptivedead time increases as a voltage of the battery increases.
 30. Theelectronic device of claim 23, wherein the battery has a battery voltageand the load has a load voltage, wherein in the adaptive mode, the boostmode regulator controls the high side switch according to an adaptivedead time, wherein the adaptive dead time changes as a voltagedifference between the battery voltage and the load voltage changes,wherein in the adaptive mode, when the low side switch switches fromconducting to not conducting, the boost mode regulator controls the highside switch to switch from not conducting to conducting after theadaptive dead time, and wherein in the adaptive mode, when the low sideswitch switches from not conducting to conducting, the boost moderegulator controls the high side switch to switch from conducting to notconducting after the adaptive dead time.